Atmosphere Pre Filter for Pro 50 (ATPRE0050) The Pre filters are used to stop small particles and dust from getting in contact with the carbon, thus preventing the premature usage of the carbon. The Pre filters are made from 100% polyester. They are sold packaged in a plastic bag to ensure they stay clean until installation. Use with Pro 50 filter. Manufacturer's Product Information MSRP each $ 9.95 UPC 628507301040 Dimensions 12 x 1 x 29.5 Case Quantity 25